A configuration and operation of a conventional optical pick-up apparatus 100 will first be described below, with reference to FIG. 1. This apparatus 100 enables information to be recorded, reproduced and erased with respect to a CD group disc 110 (e.g. CD, CD-ROM, CD-R and CD-RW) and a DVD group disc 111 (e.g. DVD, DVD-ROM, DVD-RAM, DVD-R and DVD-RW, DVD+R, DVD+RW), as well as to write/read more recently introduced Blu-ray discs and/or HD-DVD format discs, with single or multiple layer formats.
Although FIG. 1 shows both of the CD group disc 110 and the DVD group disc 111 for the purpose of illustration, as a practical matter, only one of these discs is loaded thereon at any given time. The CD group disc 110 or the DVD group disc 111 is placed on a common plane P facing an objective lens 109. On the reverse side of the plane P, recording surfaces 110a and 111a are provided. Since the CD group disc 110 has a thickness larger than that of the DVD group disc 111, the recording surface 110a of the CD group disc 110 is positioned further from the objective lens 109 than the recording surface 111a of the DVD group disc 111.
This apparatus 100 has an infrared semiconductor laser device 101 for CD (about 780 nm) and a red semiconductor laser device 102 for DVD (about 650 nm) and/or a blue laser device for Blu-ray/HD-DVD (about 405 nm) which can also be present, but is not shown in FIG. 1. In optical paths between the laser devices 101 and 102 and the discs 110 and 111, 3-beam generating diffraction gratings 103 and 104, a beam splitter 105, a collimator lens 106, a beam splitter 107, a condenser lens 112, a photodetector IC (PDIC) 113, a mirror 108 and the objective lens 109 are arranged (Lens 109 should be rotated counter clockwise by 180 degrees from the position as shown in FIG. 1). PDIC generally has a fixed photo detector pattern.
Part of the laser beam from the laser devices 101 and 102 is incident on a laser power monitoring photodetector (PMIC) 121. The photoelectrically converted output of the photodetector 121 is supplied to an automatic power controller 122 which is coupled to a laser driver 123 which drives laser devices 101 and 102.
The 3-beam generating diffraction gratings 103 and 104 form three beams from optical beams emitted from the infrared semiconductor laser device 101 and the red or blue semiconductor laser device 102, respectively. The beam splitter 105 guides the beams that have passed through the 3-beam generating diffraction gratings 103 and 104 onto the common optical axis. The collimator lens 106, the objective lens 109 and the condenser lens 112 function as a light-gathering device. The beam splitter 107 divides the reflected light from the disc 110 or 111.
The optical pick-up apparatus operates as follows: when recording, reproducing or erasing information with respect to the CD group disc 110, the infrared semiconductor laser device 101 operates. An optical beam emitted from the infrared semiconductor laser device 101, which is indicated by a solid line, is diffracted by the 3-beam generating diffraction grating 103 so as to be divided into three optical beams (a main beam as zero-order diffracted light and side beams as .+-.first-order diffracted light). These three optical beams pass through the beam splitter 105, then are converted from the divergent beams to parallel beams by the collimator lens 106, and enter into the objective lens 109 via the mirror 108 to be focused onto the CD group disc 110. Reflected light from the CD group disc 110 passes through the objective lens 109 and the mirror 108, is directed to a different direction by the beam splitter 107, and is focused onto the PDIC 113 by the condenser lens 112. From the main beam and side beams incident on the PDIC 113, an RF signal, a focus error signal and a tracking error signal are detected.
Meanwhile, when recording, reproducing or erasing information with respect to the DVD group disc 111, the red semiconductor laser device 102 operates. An optical beam emitted from the red semiconductor laser device 102, which is indicated by a dashed line, is diffracted by the 3-beam generating diffraction grating 104 so as to be divided into three optical beams (a main beam as zero-order diffracted light and side beams as .+-.first-order diffracted light). These three optical beams are directed to a different direction by the beam splitter 105, then are converted from the divergent beams to parallel beams by the collimator lens 106, and enter into the objective lens 109 via the mirror 108 to be focused onto the DVD group disc 111. Reflected light from the DVD group disc 111 passes through the objective lens 109 and the mirror 108, is directed to a different direction by the beam splitter 107, and is focused onto the PDIC 113 by the condenser lens 112. From the main beam and side beams incident on the PDIC 113, an RF signal, a focus error signal and a tracking error signal are detected. For blue medium, more photo-detector sections may be required to calibrate scattered light and for other purposes.
As described above, optical pickup apparatus 100 uses a single PDIC 113 is for optical signal reading for both DVD and CD, and with addition of a blue laser (not shown) can also provide optical signal reading for blu-ray and HD-DVD. As noted above, in typical applications, each laser beam, such as infrared (780 nm for CD), red (about 650 nm for DVD and blue (405 nm for Blu-ray and HD-DVD) is split to 3 beams by optical gratings, forming a central beam (zero order) and two side beams (first order). The center beam reads the disc data, while the side beams helps to keep the beam in the disc track.
FIG. 2(a) shows a conventional PDIC 200 having main channel PD (or PD bank) 210 and side channels PD (or PD banks) 220 and 230 along with a single diffraction grating 231. The single grating 231 is shown only to demonstrate a limitation of conventional optical pickup units. In practical applications, each laser will generally have its own diffraction grating, but a single PDIC, such as PDIC 200, will be used.
PD or PD main channel bank 210 detects the zero order beam, and side channel PD or PD bank 220 and side channel PD or PD bank 230 each detect one of the pair of first order diffracted beams. As well known in then art, when light passes through a diffraction grating, such as grating 231, different wavelengths of light are bent through a different angle, with the longest wavelength (780 nm-infrared) being bent through the largest angle while blue light (405 nm) is bent through the smallest angle, with red light falling in between. Thus, due to different wavelength for CD (780 nm), DVD (650 nm) and blue ray and HD-DVD (405 nm), even though the central beam lands at the center of the main channel photo detector 210 for each laser beam, the side beams generally land at different locations on side channel PD or PD bank 220 and side channel PD or PD bank 230 due to the wavelength difference. As shown in FIG. 2(a), since the red beam lands at the center of side channel PD or PD bank 220 and side channel PD or PD bank 230, PDIC 200 will be optimized for DVD (about 650 nm), but will provide relatively poor performance for both CD (780 nm) and blue ray and HD-DVD (405 nm).
FIG. 2(b) shows a conventional PDIC pattern layout showing PD or PD center bank 210, side channel PD or PD bank 220, and side channel PD or PD bank 230. Center (main) PD bank 210 is shown comprising sectors A, B, C and D.
For optimal performance, the side beam should land at the center of the 2 sections of the side PD pattern (i.e., between H&G for PD 220 and between F&E for PD 230). However, as shown in FIG. 2(a) for different wavelengths, the location of the side channel PDs would need to be different for the various wavelengths for the respective side beams to land at the center of the 2 sections of the side PD pattern. However, since conventional photodetector detection patterns are fixed, the PDIC 200 can only be optimized for one wavelength, such as DVD (about 650 nm) shown in FIG. 2(a), while providing relatively poor performance for the other wavelengths, such as for both CD (780 nm) and Blu-ray and HD-DVD (405 nm).